The overall objectives are to clarify the physiological functions and pharmacological actions of hormones affecting calcium metabolism and to relate this information to problems in diagnosis and treatment of disease. Principal attention is directed at parathyroid hormone (PTH) and thyrocalcitonin (TC) and their interrelations with the adrenal gland, gastro intestinal hormones, and vitamin D. Specific current projects include: 1. Pharmacology of rat TC; 2. Species crossreactivity of rat TC; 3. Variation in serum calcium from time to time and from animal to animal in relation to precision of semimicro (Technicon) and micro (Calcette) analytical determinations for calcium. 4. TC in lactating rats; 5. Mechanisms responsible for increase in C-cell count and immunoassayable TC in thyroid gland and peripheral blood of rats made goitrous by long-term iodine deficiency; 6. Protective effect of TC against experimental cardiovascular and renal calcification; 7. Relative importance of skeleton, kidney, and G-I tract in contributing to the rapid fall in serum calcium after parathyroidectomy in old and young rats; 8. Hormonal and other factors that prevent hypercalcemia during intestinal absorption of calcium after ingestion of food containing calcium; and 9. Adrenal factor that increases hypocalcemic response to parathyroidectomy in rats.